NOT APPLICABLE
NOT APPLICABLE
NOT APPLICABLE.
1. Field of the Invention
This invention relates to a method for facing a substrate and more particularly to a novel method for applying a hard facing material to a substrate to provide an improved wear resistant or cutting surface.
It is known to apply hard facing materials to surfaces of components, tools, and implements subject to wear in order to improve their wear resistant and cutting properties. An example of a hard facing material is tungsten carbide, which, in a known process, is positioned on a metal surface and then fixed in place by means of a metal layer sprayed onto the surface. The tungsten carbide may be in the form of small, irregularly-shaped lumps, or particles, or in the form of small rectangular blocks, sometimes called tips or inserts.
The tungsten carbide blocks are desirably laid in a regular pattern on the metal surface, but hitherto it has proved extremely difficult to hold the blocks in place whilst the sprayed metal layer is applied, particularly when the underlying metal substrate surface is curved such as, for example, when applying a hard facing material to a stabiliser of a drill string of the type used in oil well technology. Hitherto the blocks have been placed in the desired pattern on a sheet of adhesive masking tape and the sheet, with the blocks adhered thereto, is inverted and placed on the pre-heated substrate in the desired position. A molten metal spray, for example of a bronze alloy, is then applied to the surface, burning off the masking tape and fixing the blocks in their desired locations. It is, however, very easy for individual blocks to fall off using this method, and at best there is nearly always some movement of the blocks from their desired positions. The procedure requires great skill, and working conditions are somewhat unpleasant in view of the need to pre-heat the metal substrate to a high temperature so that the spraying process can be carried out quickly, firstly to provide good adhesion and secondly in order to avoid moving or dislodging the blocks during the spraying process.
The following prior art publications are deserving of brief discussion.
2. Description of Related Art
In United Kingdom Application GB2133062, published Oct. 2, 1968, the entire disclosure of which is incorporated herein by reference, there is described a method of providing a wear surface for the blade of a tool, which comprises the steps of inserting an inlay of hard wearing material into an undercut groove running lengthwise of the blade and heating the mass until the inlay bonds to the groove. The machining of the undercut grooves is of course a very costly and time consuming operation, and the entire tool needs to be placed in an oven at a high temperature to achieve the required bonding, which is wasteful of energy.
In GB1128880, the entire disclosure of which is also incorporated herein by reference, there is described a method of joining a metal tube to a wall, in which the tube is retained in position on the wall by tack welding, and then sprayed with molten aluminium from a gun, such that the fillet area between the arcuate surface of the tube and the wall is filled with solidified molten aluminium. The coating is continuous across the tube and of such a thickness as to serve as the essential heat transfer path from the surface of the wall to the tube. This patent is not concerned in any way with the hard facing of a substrate.
We have now discovered an improved process for hard facing a substrate which obviates many of the disadvantages of the known procedures. In this improved process, appropriately shaped bodies of the hard material are attached to the substrate and then anchored in position by the application of a molten metal.
In one aspect, the present invention provides a method of facing a substrate, which comprises attaching a body of a facing material to the substrate and filling a space around the body with a molten metal.
The invention can be used to apply a variety of facing materials to a substrate, to produce, for example, knife blades or bearings, but it is more particularly of use in the hard facing of metal components with, for example, hard facing materials such as tungsten carbide. In general, of course, the hard facing material will be harder, and/or more wear resistant, than the substrate to which it is applied. The invention will be principally described herein with reference to such hard facing materials, but it is to be understood that it is not limited thereto, and could, for example, be used to apply facing materials having other useful properties, for example, slip, or frictional characteristics, to a substrate. These and other features, aspects and advantages of the present invention, will become better understood from the following drawings, descriptions and appended claims.